Edward Thompson: Wartime C.M.E. Discussion

.... and running on the national 7'-01/4" gauge network, a most impressive sight they would've made too!

 

I misread that as 7 1/4 inch network. The world’s first sit astride commuter and intercity service.

 

Don't think it would be the first sit astride commuter and intercity service - Virgin already bl**dy well run that service pattern on the 08:15 up service from Southampton every morning ...

Tom

 

Or by a fleet of 5'2" driving wheel diameter 2-8-2s.

 

I am somewhat intrigued as to why you think they would burn less coal if the drive was to the first axle, but also somewhat wary that asking this is going to lead to yet another thread derailment.

 

Why and how?

 

Whenever someone postulates some magic, yet unquantified, efficiency saving, I always like to ponder the impact of the desired gizmo on coal consumption while a loco is standing at rest in a yard or station, as happened to a large extent, and wonder to what extent the likes of compounding, improved draughting etc, will lead to coal savings for a stationary locomotive.

Normally such thoughts lead inevitably on to the fact that the CMEs of old were, in the main, smart blokes with a business interest in reducing overall costs, and rarely took the magic nostrums suggested.

Tom

 

In the Leader trials, while Leader managed an impressive 1% thermal efficiency, the Mogul it was tried against managed 4%

Now if you could up it to 5% thats a 25% coal saving.

It is also 25% less ash to dispose of and 25% less loco coal to be hauled, 25% less coal that needs handling etc etc...........................

 

You're about to tell us it had a great personality, aren't you...

I did not know this, and it makes a huge difference. We've all believed that Thompson wanted Great Northern to look how it turned out, a somewhat brutalist look at best. To be told that he actually wanted to make it pretty but was thwarted changes things a lot. Can you post any pictures of what was intended?

 

I heard it had a great sense of humour...

 

I am stunned. One of your "improved" locomotive pictures actually improves the appearance of a locomotive!

 

I don't think those figures are correct

a well designed steam loco will attain around 10% TE
an exceptional design will achieve 13/14%

 

Under the fair use act, and purely for illustrative purposes, I can. Taken from RCTS vol 2A, as it happens:



A quick pointer to some relevant info. Bear in mind Thompson’s retirement came in 1946.


These two versions appear after Great Northern had been rebuilt in 1945. Note that there are two versions of the wheelbase and cylinder arrangement.

This was a fundamental issue all through Thompson’s tenure from the first emergence of A class (later A2/2) Thane of Fife. Both the Thompson style and Gresley style wheelbases were always drawn for comparison.

Robert Thom intiated the equal length connecting rod feature, if we believe a couple of sources. Nothing to suggest that isn’t true; what is true is that Thompson liked this and pressed for this wheelbase arrangement on basis of valve events.

It also has some minor advantages in maintenance aspects. Access to all parts of the front bogie was possible without having to interfere with or be restricted by in some way, the cylinders.



This version came after that above and actually has an outline very similar to the P2 arrangement of smoke deflectors, albeit with a full smoke box and a sloping top reminiscent of the Duchesses.



This was more less the final revised version of Thompson’s A1. Note that it moves the front bogie back to the Gresley position. Effectively, here was the final version of Gresleys original A1 Pacific, with the last major change being divided drive and three sets of walschaerts valve gear.

We have to remember that Thompson and the drawing office were well aware of the main advantage of this front end - smoke deflection.

All of the Thompson Pacifics had some form of smoke deflector by the end of steam. They all to different degrees suffered from drifting smoke obscuring the drivers view (A2/2s the worst for this).

The A1/1 and Thompson’s other A2 classes proved the robustness of the divided drive setup. That this was retained through to Peppercorns era is significant. That it was also modified to make more compact locomotives is also significant.

The position of the front bogie was not an aesthetic choice but done on maintenance grounds. One could argue that for Peppercorns team, the benefits of the more compact wheelbase outweighed the minor gains in maintenance advantages when it came to works visits.

I don’t believe we’d disagree that the Peppercorn A1 is one of the finest locomotives ever to operate in this country. It retained the ethos of Thompson’s approach to cylinders and valve gear together with smokebox and boiler design, albeit frames and cartazzi setup was more akin to the A2 sub classes.

Within a six year period the LNER had done some remarkable development work on their Pacifics, using the A2/2s as Guinea pigs and developing their ideas forward with every design.

The one reversion of the bogie position does not undo the fact that all other aspects of Thompson’s Pacific designs - and crucially, his divided drive layout - were taken forward with minimal changes.

 

The steam piping can be shorter and more direct.It is easier to make a compound scheme as outside cylinder distance cab be 6 feet 2 instead of 6feet 8.

 

Please take this to a thread on locomotive development. Thank you.

 

Virgin?

 

Sorry, I regard this as a false argument. Taken from the other side" what effect would a very inefficient locomotive have on coal consumption while it is standing at rest in a yard or station"?
In 150 years of steam locomotive development all improvement was meant for running locomotives, let's stick to that.
Kind regards
Jos

 

I dunno, its a fair point. Lets say a hypothetical improvement will reduce coal consumption by 10% when the boiler is steaming near its limits, working hard, but is of marginal benefit in other circumstances. and lets say, because you rarely get something for nothing, it adds an increment in cost to every overhaul, just from the extra time to remove, service and replace that improvement. On a locomotive that is steaming hard for the majority of its life the coal consumption saving may well be worth the increase in maintenance costs. On a locomotive that has duties that require steaming near its limits only part of the time the fuel saving may be quite marginal and therefore the improvement will not benefit TCO in that application.